The maximum mean body weights of rats attained during the course of two-year studies increased by about 20% from 1975 to 1985. Higher body weights will lead to increases in the incidences of mammary tumors, pituitary tumors, and possibly other tumors. Modification of diet and feeding procedures may slow the growth and lower the maximum body weight attained which in turn may decrease the incidences of spontaneous tumors. Lower protein diet may decrease the incidence and severity of kidney disease. The purpose of this study is to determine the feasibility of a 15% protein diet (NTP-88) with restricted feeding from 4 p.m. 1 to 8 a.m. in lowering the maximum body weights and decreasing the severity of nephrosis of rats in comparison with Ad libitum feeding and 24% protein diet ;(NIH-07). Groups of 25M + 25F F344 rats housed 5/cage by sex were fed NIH-07 or NTP-88 diet Ad libitum or 4 p.m. to 8 a.m. daily. Body weights and feed consumptions were determined at one- to eight-week intervals. Water consumption and urine analysis were done at selected intervals and at the end of the 24 month study. Kidneys are being processed for microscopic evaluation of severity of kidney disease.